Semiconductor substrates are typically batch processed in vacuum chemical vapor deposition (V-CVD) diffusion furnaces to form a thin-film of selected characteristics on the semiconductor substrates during the various phases of the integrated circuit fabrication processes. The batch of substrates to be processed is removably disposed into a longitudinally extending reaction chamber maintained at a selected temperature and vacuum condition for the particular V-CVD process being run, and one or more reactants in gas phase are controllably injected into the longitudinally extending reaction chamber via gas injectors. A portion of the one or more reactants in gas phase pyrolytically decomposes and is surface catalized by the substrates to deposit intended thin-film in solid phase thereon. Another portion of the one or more reactants in gas phase is surface catalyzed by the surfaces of the reaction chamber and gas injectors to deposit material thereon that must be removed at regular intervals during which the V-CVD diffusion furnace is inoperative for routine down-time cleaning. Reference may be had to co-pending application Ser. No. 552,454, entitled MODULAR V-CVD DIFUSION FURNACE, invented by the same inventive entity and assigned to the same assignee as the instant invention, incorporated herein by reference, for its disclosure of a novel diffusion furnace operative to extend the interval between routine down-time cleaning by a factor of between 20 and 50 over the theretofore known furnaces. The remaining portion of the one or more reactants in gas phase, typically the major portion of the reactants injected into the reaction chamber, is discharged as a waste-effluent stream that forms into flaky, porous, and powdery deposits in the vacuum system itself.
Typically, from 70 to 85% of the one or more reactants in gas phase injected into the reaction chamber exit as a waste-effluent stream into the vacuum system. This commonly necessitates cleaning the filter of the vacuum system once per shift, and necessitates changing the oil of the vacuum system once every several shifts. These oil and filter changes are not only messy, particularly in view of the clean-room environment in which the CVD processes are run, but also are disadvantageous due to the labor and materials costs incurred for each such change. Moreover, the vacuum pump itself must commonly be changed at least on a quarterly basis. Not only are considerable labor and material costs incurred in changing the vacuum pump, but it commonly takes approximately from one-half to one shift to replace the pump, and approximately another one-half shift to once again start up the CVD processes, during which times the furnace is inoperable with consequent loss of revenues and material throughput.